Mike is shown being a college student in the 1970s. Assuming that he went to college straight from high school (or even after an open year) he would still be in his early 20s when the series began. Rob Reiner is clearly older than the character would be and he seems to be a very poor student as it takes him nearly six years to complete college (despite going full time) only to obtain a job that would require just a four-year degree.
Throughout the first five seasons,it appears that Mike and Gloria's bedroom is on the opposite side of the wall from Archie and Edith's bedroom.
But in later episodes both bedrooms appear to be directly across the hall from eachother.
The house in the opening credits (that is presumably supposed to be Archie and Edith Bunker's house) does not come anywhere near matching the studio sets that represent the house in the show. For example, window placement and size is completely wrong, and the sets depict the house as having a large front porch whereas, the house in the credits has only a small stoop.